1. Field of the Invention
The present invention relates generally to mass transfer and heat exchange columns and, more particularly, to liquid distributors used in such columns and methods of distributing liquid using such liquid distributors.
2. The Prior Art Background
In mass transfer and heat exchange columns, liquid and vapor streams are brought into contact with each other to effect mass transfer and/or heat exchange between the liquid and vapor. One or more beds of structured or random packing are typically used to facilitate intimate contact between the liquid and vapor and thereby enhance the desired mass transfer and/heat exchange. The liquid stream typically descends through the packing bed while the vapor stream ascends through the packing bed in countercurrent relationship to the flow of the liquid stream.
Uneven horizontal distribution of the liquid stream as it enters the packing bed is undesirable because it reduces the area of contact between the liquid and vapor and thus decreases the mass transfer and/or heat exchange between the liquid and vapor. To ensure proper operation of the column, it is also important to ensure that the ratio of liquid to vapor is constant over the cross-section of the column. For this reason, it is important to have an even distribution of liquid as it enters the packing bed. Various types of liquid distributors are used in attempts to facilitate the horizontal distribution of liquid as it enters the packing bed from an overlying region in the column. In general, these distributors deliver the liquid to the packing bed at a number of spaced apart locations, commonly referred to as “drip-points.” The drip-point density is a measure of the number of drip-points per unit area and is commonly used to measure the distribution performance of liquid distributors.
One known type of liquid distributor uses a plurality of elongated, parallel troughs to horizontally distribute the liquid to the underlying packing bed. Liquid is distributed to the troughs by a feed box that extends perpendicularly to the parallel troughs. In one arrangement, the feed box is positioned on top of the parallel troughs and delivers liquid to the parallel troughs through a plurality of holes in the floor and/or side walls of the feed box. In another arrangement, the parallel troughs extend outwardly from the sides of the feed box and liquid flows into the parallel troughs through openings in the side walls of the feed box. In one general type of distributor, such as disclosed in U.S. Pat. No. 4,855,089 to Michels and in U.S. Pat. No. 4,816,191 to Berven et al., splash baffles are spaced outwardly from the side walls of the parallel troughs to receive liquid exiting from the parallel troughs. The liquid then flows down the splash baffles and drips into the packing bed along a drip line. It is also known to include a number of horizontally extending corrugations in the splash baffles. In a further type of distributor disclosed in EP 0 42 615 A2, drip tubes descend from the parallel troughs and deliver liquid to a multi-port distributor plate that multiplies the number of drip points into the underlying packing bed.
One problem associated with known types of liquid distributors is the difficulty in ensuring uniform horizontal distribution of liquid at low liquid flow rates. A need has thus developed for a liquid distributor that is capable of facilitating uniform liquid mixing and horizontal distribution at low liquid flow rates.